A study performed in 2005 claims to have acquired results that do not support the sexy sons hypothesis like the 2013 Nelson study did. The study performed by Lars Gustafsson and Anna Qvarnstrom showed that collared flycatchers did not inherit sexiness from their fathers. A male collared flycatcher’s attractiveness is determined largely by the size of its white forehead patch. Larger patches correlates to greater reproductive success for males. A major problem that the research team attempted to analyze was the problem with the tradeoff between reduced fecundity (ability to produce an abundance of offspring) and the sexiness of their sons.
What they discovered was that the flycatchers who were in polygamous relationships actually produced sons with smaller forehead patches than those of monogamous relationships. Additionally, because the monogamous sons had larger forehead patches and were thus more attractive, a higher proportion of their sons actually went into polygamous relationships contrary to what their fathers had done. One important point concerning the reason behind this discrepancy is found.
The paternal care for the polygamous lineage offspring was significantly lower than that of monogamous relationships due to the spread of time among the many offspring. Males who were indeed more attractive produced less attractive sons because there was an apparent tradeoff between offspring sexiness and reproductive success. This brings up an important point: when the attractiveness of the offspring is dependent on both environmental factors and the attractiveness of the parent, then the costs of polygyny are unlikely to outweigh the initial genetic advantage.
This can be tied to the Nelson study which demonstrates that many epigenetic factors also play a role in the development of sexy offspring. In this case, the flycatchers were raised with little paternal care which led to underdevelopment of their potentially attractive features. Paternal care’s importance is further backed up in the Aguilar study for pathogen avoidance. The pathogen avoidance model was created in response to the sexy sons hypothesis to acknowledge some apparent flaws.
Popularized by Craige Loehle in 1997, the theory states that females can avoid parasites by choosing showier males and that the benefit of choosing showier males is to benefit the female’s reproductive success rather than the fitness of offspring. 4 main problems Loehle points out about the good genes model are that secondary sex traits don’t signal fitness levels, assumptions must be made about gene linkages between female preference and secondary sex traits, females must prefer showier trait when it first occurs which is highly unlikely, and females must show preference for an unusual trait.
Good genes aren’t always signaled by showy or ornamental traits as is shown in the fact that males with greater expression of secondary sex traits likely live shorter lives (Nelson, et al. 2013). Thus, it is far more likely that over the course of many years, females will recognize this fact rather than viewing more ornamental males to be better. The second point adds on to this fact as female preference to the trait must be linked to the presence of the trait otherwise the trait would not even be viewed as “ornamental” or “showy” which is highly unlikely.
Additionally, the third and fourth point tie together in that showier traits must be prefered which is also unlikely as when the trait first emerges, it is viewed as radical and different which should signal a defect in the male and thus counteracts the interactions between individuals in the sexy sons hypothesis. The pathogen avoidance model can be inferred in many examples in nature such as in satin bowerbirds (Borgia and Collis, 1990). In these birds, females can be seen to shake after intercourse in attempts to rid themselves of parasites.
This can be explained by the fact that females are the primary caretakers of most animal species on the planet and that a parasite on the female will likely also transmit itself to the young; thus females must select for more healthy males in order to protect themselves and eventually their offspring from pathogens. The primary difference between this model and the sexy sons model is that safety from disease is the primary focus rather than the fitness of the offspring.
This can only hold true if the degree to which an individual is ill can be seen through their expression of secondary sex traits. The traits are what are called honest indicators as when infection status increases, the expression of the traits decreases. It has been found that males infected with a pathogen usually received less physical contact from females which backs up this model of sexual selection. Analysis of Pathogen Avoidance Model